X-ray diagnostic apparatus and correction method

Abstract

To suppress an influence of a change in an imaging condition from a change in image density in a time direction of an X-ray image by a contrast medium.SOLUTION: An X-ray diagnostic apparatus includes an X-ray tube, an X-ray detector, an image generation part, an acquisition part, and a correction part. The X-ray tube irradiates a subject injected with a contrast medium with an X-ray. The X-ray detector detects the X-ray emitted from the X-ray tube and penetrating the subject. The image generation part generates an X-ray image of the subject on the basis of the output of the X-ray detector. The acquisition part acquires an index on the brightness of the X-ray image. The correction part corrects a brightness value of the X-ray image for the latest index on the basis of a reference index before injection of the contrast medium and the latest index after the injection of the contrast medium is started of the acquired indexes.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to an X-ray diagnostic apparatus and a correction method.

Background Art

[0002] A myocardial blood flow measurement analysis method using X-ray images of the heart region injected with a contrast agent has been proposed. In this method, a plurality of frames of X-ray images after contrast agent injection are acquired by an X-ray diagnostic apparatus, and image analysis is performed using the change in image density in the time direction of the X-ray images. This method assumes that the imaging conditions do not change in the time direction. This assumption is provided in consideration of the fact that if the image density of the entire X-ray image changes according to the change in imaging conditions, it becomes difficult to utilize the change in image density due to the contrast agent.

[0003] On the other hand, in daily clinical practice, an X-ray diagnostic apparatus often changes the imaging conditions in the time direction so as to brighten the entire X-ray image darkened by the injection of a contrast agent by performing automatic brightness control. In this case, since the change in image density is affected by the change in imaging conditions, the change in image density of the X-ray image cannot be directly used for image analysis.

[0004] Therefore, it is desirable to suppress the influence of changes in imaging conditions from the change in image density in the time direction of the X-ray image due to the contrast agent.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to suppress the influence of changes in imaging conditions from the change in image density in the time direction of X-ray images by a contrast agent. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. The problems corresponding to the respective effects of the respective configurations shown in the embodiments described later can also be regarded as other problems.

Means for Solving the Problems

[0007] The X-ray diagnostic apparatus according to the embodiment includes an X-ray tube, an X-ray detector, an image generation unit, an acquisition unit, and a correction unit. The X-ray tube irradiates X-rays onto a subject into which a contrast agent is injected. The X-ray detector detects the X-rays irradiated from the X-ray tube and transmitted through the subject. The image generation unit generates an X-ray image of the subject based on the output of the X-ray detector. The acquisition unit acquires an index related to the brightness of the X-ray image. The correction unit corrects the luminance value of the X-ray image with respect to the latest index based on the reference index before the injection of the contrast agent and the latest index after the start of the injection of the contrast agent among the acquired indexes.

Brief Description of the Drawings

[0008]

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MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, an X-ray diagnostic apparatus and a correction method according to each embodiment will be described with reference to the drawings. First, terms used in the following description are defined as follows. The pulse rate is an index that defines the frequency of irradiating a subject with X-rays, and is expressed in units (times / second, times / minute) or (times / heartbeat) as the number of X-ray irradiations per unit time (1 second or 1 minute) or per heartbeat. The frame rate, which represents the number of image frames captured per unit time, is substantially equivalent to the pulse rate. Note that when irradiating X-rays defined by the pulse rate, not only the form of generating X-rays of the pulse rate from the X-ray tube and directly irradiating the subject with them, but also the form of continuously generating X-rays and forming X-rays defined by the pulse rate by an X-ray shutter or the like and irradiating the subject with them is included. Perfusion represents the flow of blood to the myocardium. The R wave represents the peak wave of the electrocardiogram waveform. The RR interval represents the time interval between R waves. mA is the tube current flowing between the electrodes of the X-ray tube and is used as an index representing the height of pulsed X-rays. The pulse width represents the duration of one pulse of X-rays, and the unit is msec. mAs is the tube current-time product obtained by multiplying the tube current and the pulse width, and is used as an index representing the intensity of X-rays. In the following description, components having substantially the same functions and configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0010] <First Embodiment> FIG. 1 is a block diagram showing an example of the configuration of an X-ray diagnostic apparatus 1 according to the first embodiment. The X-ray diagnostic apparatus 1 includes an imaging apparatus 10, an injector 40, a bed apparatus 50, and a console apparatus 70. The imaging apparatus 10 includes a high-voltage generator 11, an X-ray generation unit 12, an X-ray detector 13, a C-arm 14, a state detector 141, and a C-arm drive device 142.

[0011] The high-voltage generator 11 generates a high voltage applied between the anode and the cathode to accelerate the thermoelectrons generated from the cathode of the X-ray tube, and outputs it to the X-ray tube.

[0012] The X-ray generation unit 12 includes an X-ray tube that irradiates the subject P with X-rays, and an X-ray aperture that has a function of limiting the X-ray irradiation field or attenuating X-rays for a part of the irradiation field.

[0013] The X-ray tube generates X-rays. Specifically, the X-ray tube is a vacuum tube that holds a cathode that generates thermoelectrons and an anode that receives the thermoelectrons flying from the cathode and generates X-rays. For example, there is a rotating anode type X-ray tube that generates X-rays by irradiating thermoelectrons onto a rotating anode. The X-ray tube is connected to the high voltage generator 11 via a high voltage cable. A tube voltage is applied between the cathode and the anode by the high voltage generator 11. When the tube voltage is applied, thermoelectrons fly from the cathode toward the anode. When thermoelectrons fly from the cathode toward the anode, a tube current flows. By applying a high voltage from the high voltage generator 11 and supplying a filament current, thermoelectrons fly from the cathode toward the anode, and when the thermoelectrons collide with the anode, X-rays are generated.

[0014] The X-ray aperture is located between the X-ray tube and the X-ray detector 13, and generally includes aperture blades, an additional filter, and a compensating filter. The X-ray aperture narrows down the X-rays generated by the X-ray tube so that only the region of interest of the subject P is irradiated by shielding the X-rays outside the opening region. For example, the X-ray aperture has aperture blades made of four lead plates, and by sliding these aperture blades, the region shielded from X-rays can be adjusted to an arbitrary size. The aperture blades of the X-ray aperture are driven by a drive device (not shown) according to the region of interest input by the operator from the input interface 73. In addition, an additional filter for adjusting the total filtration of X-rays can be inserted into the X-ray aperture from a slit. Further, a lead mask or a compensating filter used during X-ray inspection can be inserted into the X-ray aperture from an accessory insertion port. Note that the compensating filter may include an ROI (Region Of Interest) filter that has a function of attenuating or reducing the irradiated X-ray dose.

[0015] The X-ray detector 13 detects the X-rays that are irradiated from the X-ray tube and have passed through the subject P. As such an X-ray detector 13, those that directly convert X-rays into electric charges and those that convert them into light and then into electric charges can be used. Here, the former will be described as an example, but the latter may also be used. That is, the X-ray detector 13 includes, for example, a planar FPD (Flat Panel Detector) that converts the X-rays passing through the subject P into electric charges and accumulates them, and a gate driver that generates drive pulses for reading out the electric charges accumulated in this FPD. The FPD is configured by two-dimensionally arranging minute detection elements in the column direction and the line direction. Each detection element includes a photoelectric film that senses X-rays and generates electric charges according to the incident X-ray dose, a charge storage capacitor that stores the electric charges generated in this photoelectric film, and a TFT (Thin Film Transistor) that outputs the electric charges stored in the charge storage capacitor at a predetermined timing. The accumulated electric charges are sequentially read out by the drive pulses supplied by the gate driver.

[0016] At the subsequent stage of the X-ray detector 13, there are provided a projection data generation circuit and a projection data storage circuit (not shown). The projection data generation circuit includes a charge-voltage converter that converts the electric charges read out in parallel from the FPD in units of rows or columns into voltages, an A / D converter that converts the output of this charge-voltage converter into a digital signal, and a parallel-serial converter that converts the digitally converted parallel signal into a time-series serial signal. The projection data generation circuit supplies this serial signal as time-series projection data to the projection data storage circuit. The projection data storage circuit sequentially stores the time-series projection data supplied from the projection data generation circuit to generate two-dimensional projection data. This two-dimensional projection data is output as the X-ray detection result to the console device 70 and stored in the memory 71.

[0017] The C-arm 14 has a configuration that enables X-ray imaging of the subject P on the top plate 53 by holding the X-ray generation unit 12 and the X-ray detector 13 so as to face each other with the subject P and the top plate 53 interposed therebetween. In the following description, a ceiling-suspended type C-arm will be described as an example, but it is not limited thereto, and for example, a floor-standing type C-arm may also be used.

[0018] Specifically, the C-arm 14 is movable along the major axis direction and the minor axis direction of the top plate 53. Further, the C-arm 14 is supported by a support arm via a holding portion. The support arm has a substantially arc shape, and the proximal end is attached to a movement mechanism for a rail provided on the ceiling. The C-arm 14 is rotatably held by the holding portion about an axis in the X direction that is orthogonal to both the Y direction perpendicular to the top plate 53 and the Z direction along the major axis direction of the top plate 53. Further, the C-arm 14 has a substantially arc shape centered on the Z axis and is held by the holding portion so as to be slidable along the substantially arc shape. That is, the C-arm 14 can perform a sliding operation centered on the Z axis. Further, the C-arm 14 can perform a rotational operation (hereinafter referred to as "main rotational operation") about an axis in the X direction centered on the holding portion, and enables observation of an X-ray image from various angular directions by a combination of sliding and this rotation. Furthermore, the C-arm 14 can also rotate about an axis in the Y direction, whereby, for example, the rotation center axis of the above-described sliding operation can be set in the X direction. Note that the imaging axis passing through the X-ray focus of the X-ray generation unit 12 and the center of the detection surface of the X-ray detector 13 is designed to intersect at a single point with the rotation center axis of the sliding operation and the rotation center axis of the main rotational operation. Generally, the intersection point is called an isocenter. The isocenter does not displace even when the C-arm 14 performs the above-described sliding operation or main rotational operation. Therefore, when an area of interest is located at the isocenter, observation of the area of interest becomes easy in a moving image of a medical image obtained by the sliding operation or the main rotational operation of the C-arm 14.

[0019] Such a C-arm 14 is provided with a plurality of power sources for realizing operations related to a support arm under the rail, an axis in the X direction, an axis in the Y direction, and an axis in the Z direction at appropriate locations. These power sources constitute the C-arm drive device 142. The C-arm drive device 142 reads a drive signal from the drive control function 742 and causes the C-arm 14 to perform a sliding motion, a rotational motion, and a linear motion. Further, the C-arm 14 is provided with state detectors 141 for detecting information on its angle, posture, and position, respectively. The state detector 141 is composed of, for example, a potentiometer for detecting a rotation angle or a movement amount, an encoder which is a position detection sensor, and the like. As the encoder, for example, a so-called absolute encoder such as a magnetic type, a brush type, or a photoelectric type can be used. Further, as the state detector 141, various types of position detection mechanisms such as a rotary encoder that outputs a rotational displacement as a digital signal or a linear encoder that outputs a linear displacement as a digital signal can be appropriately used.

[0020] When taking a contrast angiography X-ray image of the subject P, the injector 40 injects a contrast agent into the subject P according to the injection amount and the injection speed communicated from the imaging control function 743.

[0021] The bed device 50 is a device for placing and moving the subject P, and includes a base 51, a bed drive device 52, a top plate 53, and a support frame 54.

[0022] The base 51 is a housing installed on the floor surface and supporting the support frame 54 so as to be movable in the vertical direction (Y direction).

[0023] The bed drive device 52 is housed in the housing of the bed device 50 and includes a motor or an actuator that moves the top plate 53 on which the subject P is placed in the longitudinal direction (Z direction) of the top plate 53. The bed drive device 52 reads a drive signal from the drive control function 742 and moves the top plate 53 in the horizontal direction or the vertical direction with respect to the floor surface.

[0024] The top plate 53 is provided on the upper surface of the support frame 54 and is a plate on which the subject P is placed.

[0025] The support frame 54 movably supports the top plate 53 on which the subject P is placed. Specifically, the support frame 54 is provided on the upper part of the base 51 and slidably supports the top plate 53 along its longitudinal direction.

[0026] The console device 70 includes a memory 71, a display 72, an input interface 73, a processing circuit 74, and a network interface 76.

[0027] The memory 71 is a storage device such as a ROM (Read Only Memory), a RAM (Random Access Memory), an HDD (Hard Disk Drive), an SSD (Solid State Drive), and an integrated circuit storage device that stores various information. Further, the memory 71 may be a drive device or the like that reads and writes various information to and from portable storage media such as a CD-ROM drive, a DVD drive, and a flash memory. Note that the memory 71 does not necessarily have to be realized by a single storage device. For example, the memory 71 may be realized by a plurality of storage devices. Also, the memory 71 may be in another computer connected to the X-ray diagnostic apparatus 1 via the network Nw.

[0028] The memory 71 stores various programs such as the processing program of the X-ray diagnostic apparatus 1, and various data such as various information used in processing, data during processing, and data after processing. Note that this processing program may be stored in the memory 71 in advance, for example. Also, for example, it may be stored and distributed in a non-transitory computer-readable storage medium, and read from the non-transitory computer-readable storage medium and installed in the memory 71. Further, examples of the various data include medical images such as projection data before image processing, X-ray images and contrast images after image processing. Note that the contrast image is an X-ray image obtained by performing imaging on the heart region of the subject with a contrast agent injected. The X-ray irradiated from the X-ray tube passes through the contrast agent present in the heart region of the subject, greatly changing its intensity, and enters the X-ray detector 13. Therefore, in the contrast image, in addition to the background such as the bones of the subject, blood vessels and myocardium in the heart region of the subject are reflected.

[0029] The program causes the computer to realize, for example, a function of acquiring an index related to the brightness of an X-ray image, and a function of correcting the luminance value of the X-ray image with respect to the latest index based on the reference index before injection of the contrast agent and the latest index among the indexes. To supplement, as such a program, for example, a program that is installed in the computer in advance from a network or a non-transitory computer-readable storage medium and causes the computer to realize each function of the medical image processing apparatus 77 is used. The memory 71 is an example of a storage unit.

[0030] The display 72 is composed of a display main body that displays various types of information such as medical images, an internal circuit that supplies a display signal to the display main body, and peripheral circuits such as connectors and cables that connect the display main body and the internal circuit. The internal circuit generates display data by superimposing additional information such as subject information and projection data generation conditions on the image data supplied from the processing circuit 74, performs D / A conversion and TV format conversion on the obtained display data, and displays it on the display main body. For example, the display 72 outputs a medical image generated by the processing circuit 74, a GUI (Graphical User Interface) for receiving various operations from the operator, and the like. For example, the display 72 is a liquid crystal display or a CRT (Cathode Ray Tube) display. Also, the display 72 is an example of a display unit. Also, the display 72 may be a desktop type, or may be configured by a tablet terminal or the like that can communicate wirelessly with the console device 70 main body. The display 72 is an example of a display unit.

[0031] The input interface 73 performs operations such as input of subject information, setting of imaging conditions, and input of various command signals. The subject information includes, for example, subject ID, subject name, date of birth, age, weight, gender, examination site, etc. Note that the imaging conditions include X-ray conditions. The input interface 73 is connected to input devices such as a trackball, switch buttons, mouse, keyboard, touch pad for performing input operations by touching the operation surface, and a touch panel in which the display screen and the touch pad are integrated, for example, to perform operations such as instructing the movement of the C-arm 14 and setting the region of interest (ROI). Also, the input device connected to the input interface 73 may be an input device provided in another computer connected via a network Nw or the like. The input interface 73 is connected to the processing circuit 74, converts the input operation received from the operator into an electrical signal, and outputs it to the processing circuit 74. Also, the input interface 73 may be configured by a tablet terminal or the like capable of wireless communication with the console device 70 main body. Also, in this specification, the input interface 73 is not limited to those equipped with physical operation components such as a mouse and a keyboard. For example, an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs this electrical signal to the processing circuit 74 is also included in the examples of the input interface 73.

[0032] The processing circuit 74 controls the operation of the entire X-ray diagnostic apparatus 1 in response to the electrical signal of the input operation output from the input interface 73. For example, as hardware resources, the processing circuit 74 includes processors such as a CPU, an MPU, and a GPU (Graphics Processing Unit), and memories such as a ROM and a RAM. The processing circuit 74 is a processor that realizes a system control function 741, a drive control function 742, a photographing control function 743, an image processing function 744, an acquisition function 745, a correction function 746, and a display control function 747 corresponding to the program by calling and executing the program in the memory 71. In FIG. 1, the system control function 741, the drive control function 742, the photographing control function 743, the image processing function 744, the acquisition function 745, the correction function 746, and the display control function 747 are described as being realized by a single processing circuit 74. However, it is also possible to configure a processing circuit by combining a plurality of independent processors, and each function may be realized by each processor executing a program. Further, the system control function 741, the drive control function 742, the photographing control function 743, the image processing function 744, the acquisition function 745, the correction function 746, and the display control function 747 may be respectively referred to as a system control circuit, a drive control circuit, a photographing control circuit, an image processing circuit, an acquisition circuit, a correction circuit, and a display control circuit, and may be implemented as individual hardware circuits.

[0033] The system control function 741, for example, once stores the command signal input from the input interface 73 by the operator and information such as various initial setting conditions, and then transmits this information to each processing function of the processing circuit 74.

[0034] The drive control function 742 controls the C-arm drive device 142 and the bed drive device 52, for example, using the information regarding the drive of the C-arm 14 and the top plate 53 input from the input interface 73. For example, the drive control function 742 controls the movement and rotation of the imaging device 10 and the movement and tilt of the bed device 50.

[0035] The imaging control function 743 reads information from, for example, the system control function 741, and controls imaging conditions (X-ray conditions) such as tube voltage, tube current, pulse width, pulse rate, and irradiation time in the high-voltage generator 11. The imaging conditions may include the tube current-time product (mAs) obtained by multiplying the tube current by the pulse width. Further, the imaging control function 743 may perform automatic brightness control (ABC) for optimizing the luminance of the X-ray image. The automatic brightness control controls the imaging conditions (X-ray conditions) so as to match the luminance value of the current X-ray image to a set value. As the luminance value of the current X-ray image, for example, a value obtained by averaging the luminance values acquired from a part or all of the regions of the X-ray image can be used. The automatic brightness control can brighten the entire X-ray image by changing the imaging conditions, for example, when the entire X-ray image becomes dark due to the injection of a contrast agent. When changing the imaging conditions, it is preferable to fix the tube voltage and change the tube current-time product (mAs). When changing the tube current-time product, at least one of the tube current and the pulse width may be changed. Further, the imaging control function 743 controls imaging conditions such as the pulse rate based on the injection start signal output from the injector 40 at the time of starting the injection of the contrast agent from the injector 40 into the subject P, the injection end signal output from the injector 40 at the time of ending the injection of the contrast agent into the subject P, and the electrocardiogram (ECG) of the subject P measured by an electrocardiograph (not shown). The imaging control function 743 and the processing circuit 74 are an example of an imaging control unit that executes automatic brightness control for controlling the luminance of the X-ray image of the subject P by adjusting the imaging conditions of the X-ray image.

[0036] The image processing function 744 performs image processing such as filtering processing on the projection data in the memory 71, for example, to generate an X-ray image, and stores the X-ray image in the memory 71. Examples of the X-ray image generated from the projection data include medical images such as an X-ray image before injection of a contrast agent and an X-ray image (contrast image) after the start of injection of the contrast agent. The image processing function 744 and the processing circuit 74 are an example of an image generation unit that generates an X-ray image of the subject P based on the output (detection result) of the X-ray detector 13. Also, for example, the image processing function 744 and the processing circuit 74 are an example of an image generation unit that sequentially generates a plurality of frames of X-ray images along a time series based on the output of the X-ray detector 13.

[0037] The acquisition function 745 acquires an index related to the brightness of the X-ray image. For example, the acquisition function 745 may acquire the index for each frame of the X-ray image. Also, for example, the acquisition function 745 may acquire the imaging conditions of the X-ray image as an index. Also, for example, the acquisition function 745 may acquire the tube current-time product as an index. The acquisition function 745 and the processing circuit 74 are an example of an acquisition unit.

[0038] The correction function 746 corrects the luminance value of the X-ray image with respect to the latest index based on the reference index before injection of the contrast agent and the latest index after the start of injection of the contrast agent among the indexes acquired by the acquisition function 745. For example, the correction function 746 may correct the luminance value so as to maintain the brightness of the X-ray image with respect to the reference index. Here, maintaining the brightness means making the brightness substantially constant. Also, for example, the correction function 746 may obtain the change ratio of the latest index with respect to the reference index and correct the luminance value based on the change ratio. The change ratio may be obtained by calculation or may be obtained by referring to a table in which the values of the reference index, the latest index, and the change ratio are associated in advance. The correction function 746 and the processing circuit 74 are an example of a correction unit.

[0039] The display control function 747 performs control such as displaying display data such as medical images in the memory 71 on the display 72. For example, the display control function 747 reads a signal from the system control function 741, acquires a desired X-ray image from the memory 71, and performs control to display it on the display 72. The display control function 747 and the processing circuit 74 are an example of a display control unit that causes the display unit to display an X-ray image whose luminance value has been corrected by the correction function 746.

[0040] The network interface 76 is a circuit for connecting the console device 70 to the network Nw and communicating with other devices such as an external medical image processing device. As the network interface 76, for example, a network interface card (NIC) can be used. In the following description, the description of the involvement of the network interface 76 in communication with other devices will be omitted.

[0041] These memory 71, display 72, input interface 73, image processing function 744, acquisition function 745, correction function 746, and display control function 747 of the processing circuit 74 constitute the medical image processing device 77. Accordingly, the descriptions of the memory 71, display 72, input interface 73, image processing function 744, acquisition function 745, correction function 746, and display control function 747 of the processing circuit 74 are descriptions of each of the X-ray diagnostic apparatus 1 and the medical image processing device 77. The medical image processing device 77 may be built in the X-ray diagnostic apparatus 1, or may be provided outside the X-ray diagnostic apparatus 1 as a device separate from the X-ray diagnostic apparatus 1.

[0042] Next, the operation of the X-ray diagnostic apparatus configured as described above will be described with reference to FIGS. 2 to 8. Note that FIGS. 2 and 6 are flowcharts, and FIGS. 3 to 5, 7, and 8 are schematic diagrams. Also, it is assumed that the subject P is placed on the top plate 53 and a catheter is inserted into the coronary artery of the heart by X-ray imaging (fluoroscopic imaging). In the first embodiment, after a low-dose preliminary contrast imaging (ST10 to ST40, ST90) for manually setting the region of interest, main contrast imaging for performing image analysis including creation of a time-concentration curve is performed (ST10 to ST30, ST50 to ST90). However, at this point, no contrast agent has been injected into the subject P.

[0043] As shown in FIG. 2, in step ST10, the X-ray diagnostic apparatus 1 executes X-ray imaging based on the imaging conditions. That is, the X-ray tube irradiates the subject P into which the contrast agent is to be injected with X-rays. The X-ray detector 13 detects the X-rays irradiated from the X-ray tube and transmitted through the subject P, and outputs the detection result of the X-rays. The processing circuit 74 generates an X-ray image of the subject P based on the output of the X-ray detector 13, and stores the X-ray image in the memory 71.

[0044] In step ST20, the processing circuit 74 acquires the X-ray image from the memory 71.

[0045] In step ST30, the processing circuit 74 determines whether the imaging conditions of the X-ray image change depending on, for example, whether the automatic brightness control is on, and if not, proceeds to step ST40. Note that the case where the determination result in step ST30 is no (ST30; No) corresponds to the off state of the automatic brightness control. Also, when proceeding to step ST40 after steps ST10 to ST30, it corresponds to preliminary contrast imaging for setting the region of interest.

[0046] In step ST40, the processing circuit 74 causes the X-ray image acquired in step ST20 to be displayed on the display 72, and proceeds to step ST90.

[0047] In step ST90, the processing circuit 74 determines whether or not the contrast imaging of the heart region of the subject P has been completed. If the determination is negative, the process returns to step ST10.

[0048] That is, when the automatic brightness control is off, the X-ray diagnostic apparatus 1 repeatedly executes the operations from step ST10 to ST40 via step ST90 during the low-dose preliminary contrast imaging in which the imaging conditions do not change. By such contrast imaging, as shown in FIG. 3, a plurality of frames of X-ray images g0, …, g1, …, g2, …, g3, …, g4, … are sequentially acquired by the processing circuit 74 and displayed on the display 72 in the time direction. In FIG. 3, the X-ray image g0 is an image acquired before the contrast imaging, and the catheter inserted into the coronary artery is observed. The X-ray image g1 is an image acquired at the start of the contrast imaging, and the contrast agent injected from the catheter reaches the myocardium through the blood vessels, and the blood vessels and the thin myocardium are observed. The X-ray image g2 is an image acquired in the middle of the contrast imaging, and the blood vessels and the thick myocardium are observed. The X-ray image g3 is an image acquired at the end of the contrast imaging, and myocardial perfusion occurs in which the contrast agent flows out of the blood vessels into the myocardium, and the myocardium with a high concentration of the contrast agent is observed. The X-ray image g4 is an image acquired after the end of the contrast imaging, and the myocardium with a low concentration of the contrast agent is observed because the contrast agent has not completely flowed out of the myocardium.

[0049] Such X-ray images include a contrast region where a contrast agent reaches during the contrast imaging period and a background region where the contrast agent does not reach during the contrast imaging period. For example, as shown in the upper left of FIG. 4, the X-ray image g2 includes a heart region Ht which is a contrast region and a background region other than the heart region Ht. The heart region Ht includes a blood vessel region and a myocardial region. The catheter Ct is inserted into a blood vessel. These regions are in the same positions in other X-ray images g0, …, g1, …, g3, …, g4, …. After a low-dose preliminary contrast imaging, by observing the X-ray images g0, …, g1, …, g2, …, g3, …, g4, …, a background region of interest Bg is set in a part of the background region according to the operation of the input interface 73 by the operator. Similarly, a blood vessel region of interest Bv is set in a part of the blood vessel region, and a myocardial region of interest Myo is set in a part of the myocardial region. Here, since the contrast agent does not reach the background region of interest Bg, when the imaging conditions are constant, as shown in the upper right of FIG. 4, the image luminance is substantially constant. Since the contrast agent flows in the blood vessel region of interest Bv, as shown in the lower right of FIG. 4, the image luminance suddenly decreases after the start of the contrast imaging period and gradually recovers toward the end of the contrast imaging. Since the contrast agent reaches the myocardial region of interest Myo from the blood vessel, as shown in the lower left of FIG. 4, the image luminance gradually decreases after the start of the contrast imaging period and gradually recovers toward the end of the contrast imaging. That is, when the imaging conditions are constant (ST30; No), the background region of interest Bg, the blood vessel region of interest Bv, and the myocardial region of interest Myo change in image luminance during the contrast imaging period as shown in FIG. 5.

[0050] On the other hand, as a result of the determination in step ST30, when the imaging conditions change, the processing circuit 74 proceeds to step ST50. Note that, as a result of the determination in step ST30, when the imaging conditions change (ST30; Yes), it corresponds to the on state of the automatic luminance control. Also, when proceeding to step ST50 after steps ST10 to ST30, it corresponds to the main contrast imaging after the preliminary contrast imaging.

[0051] In step ST50, the processing circuit 74 obtains, for example, for each frame of the X-ray image, an index related to the brightness of the X-ray image. Such a step ST50 includes steps ST51 to ST53, for example, as shown in FIG. 6. That is, the processing circuit 74 refers to the memory 71 and obtains the tube current and the pulse width from the imaging conditions of the X-ray image (ST51). Further, the processing circuit 74 multiplies the obtained tube current and pulse width (ST52), and obtains the multiplication result, which is the tube current time product, as an index (ST53). Thereby, step ST50 ends.

[0052] In step ST60, the processing circuit 74 calculates, based on the obtained indexes, the change ratio of the latest index with respect to the reference index between before the injection of the contrast agent and the latest index after the start of the injection of the contrast agent. For example, when the reference index is Id0 and the latest index is Idn, the processing circuit 74 calculates the change ratio k from the formula k = Idn / Id0. Note that the reference index Id0 is the reference tube current time product before the injection of the contrast agent, and the latest index Idn is the latest tube current time product after the start of the injection of the contrast agent. The tube current time product is an example of an index corresponding to the brightness of the X-ray image. The larger the tube current time product is, the brighter the X-ray image is. The change ratio k is updated to a value corresponding to the change in the latest tube current time product for each frame of the X-ray image. For example, when the change ratio k = 1.1, the latest X-ray image is 1.1 times brighter than the reference X-ray image.

[0053] In step ST70, the processing circuit 74 corrects the luminance value of the X-ray image with respect to the latest index Idn based on the change ratio. For example, when the luminance value of the X-ray image with respect to the latest index Idn is Bn, the processing circuit 74 calculates the corrected luminance value Cn from the formula Cn = Bn / k. For example, when the change ratio k = 1.1, the corrected luminance value Cn is approximately 0.91 times the luminance value Bn before correction. Note that the formula for obtaining the corrected luminance value Cn is obtained from the relationship Id0:Idn = Cn:Bn (Cn = Bn(Id0 / Idn) = Bn / k). Thereafter, the processing circuit 74 corrects the luminance value Bn of the X-ray image with respect to the latest index to the calculated luminance value Cn.

[0054] In step ST80, the processing circuit 74 causes the display 72 to display an X-ray image having the corrected luminance value Cn, and proceeds to step ST90.

[0055] In step ST90, the processing circuit 74 determines whether or not the contrast imaging of the heart region of the subject P has been completed. If the determination result is negative, the process returns to step ST10.

[0056] That is, when the automatic brightness control is in the ON state, the X-ray diagnostic apparatus 1 repeatedly executes the operations of steps ST10 to ST30 and ST50 to ST80 via step ST90 during the contrast imaging period in which the imaging conditions change. Here, in steps ST10 to ST30, as shown in FIG. 7(a), the tube current among the imaging conditions increases in accordance with the automatic brightness control. Along with this, as shown in FIG. 7(b), the image brightness of the background region of interest Bg and the myocardial region of interest Myo increases compared to the image brightness shown in FIG. 5, and the image brightness of the entire X-ray image changes to be substantially constant. Note that the X-ray image having the image brightness shown in FIG. 7(b) is an image before correction, and since it is a normal clinical image in which the entire X-ray image darkened by the injection of the contrast agent is brightened by the automatic brightness control, it is displayed on a part of the display 72. However, as shown in FIG. 7(b), the X-ray image before correction cannot be directly used for image analysis because the image brightness of the background region of interest Bg where the contrast agent does not reach increases.

[0057] In contrast, in step ST70, as shown in FIG. 8(a), the luminance value of the X-ray image for the latest imaging conditions after the start of injection of the contrast agent is corrected to the luminance value of the X-ray image for the reference imaging conditions before injection of the contrast agent, as shown in FIG. 8(b). Note that FIG. 8(a) is the same figure as FIG. 7(b). After such correction, in the X-ray image, as shown in FIG. 8(b), the image luminance of the background region of interest Bg where the contrast agent does not reach changes substantially constantly, and thus it can be directly used for image analysis. Also, the X-ray image having the image luminance shown in FIG. 8(b) is displayed in another part of the display 72 in step ST80. For example, the corrected X-ray image may be displayed in a part of the peripheral region within the display 72. At this time, on the display 72, the first display region of the X-ray image before correction (normal clinical image) is located, for example, at a substantially central portion of the display 72 and has a larger area than the second display region of the corrected X-ray image. However, it is not limited to this, and the sizes and arrangements of the first display region and the second display region can be set as appropriate. Also, the display of the corrected X-ray image may be omitted.

[0058] On the other hand, after step ST80, if it is determined in step ST90 that the contrast imaging has ended, the processing circuit 74 ends the processing.

[0059] As described above, according to the first embodiment, the X-ray tube irradiates the subject P into which the contrast agent is injected with X-rays. The X-ray detector 13 detects the X-rays irradiated from the X-ray tube and transmitted through the subject P. The processing circuit 74 generates an X-ray image of the subject P based on the output of the X-ray detector 13. The processing circuit 74 obtains an index related to the brightness of the X-ray image. The processing circuit 74 corrects the luminance value of the X-ray image for the latest index based on the reference index before injection of the contrast agent and the latest index after the start of injection of the contrast agent among the obtained indexes. Thus, with the configuration of correcting the luminance value of the X-ray image for the latest index based on the reference index and the latest index related to the brightness of the X-ray image, the influence due to the change in the imaging conditions can be suppressed from the change in the image density in the time direction of the X-ray image caused by the contrast agent.

[0060] Regarding this effect, it will be supplemented and explained with reference to FIGS. 9 and 10. In FIG. 9, the X-ray image g10 is an example of an image before correction obtained in the middle stage of contrast imaging among a plurality of frames of X-ray images obtained by contrast imaging. It is assumed that in the heart region Ht where the catheter Ct is inserted in the X-ray image g10 before correction, a vascular region of interest Bv and a myocardial region of interest Myo are set. Also, it is assumed that a background region of interest Bg is set in a part of the background region different from the heart region Ht in the X-ray image g10 before correction. By performing image analysis on such X-ray images before correction for each frame, as shown in FIG. 10, a time-concentration curve is obtained with the horizontal axis representing time and the vertical axis representing the average pixel value within each region of interest Bv, Myo, Bg. Generally, in a time-concentration curve, it is possible to identify characteristic quantities related to the flow of the contrast agent. Examples of such characteristic quantities include, for example, the inflow time of the contrast agent. There are several methods for identifying the inflow time of the contrast agent, and here three typical methods will be described. The first is a method of identifying the time T0 of the peak value (maximum value) of the time-concentration curve as the inflow time of the contrast agent at the pixel, which is also called TTP (Time To Peak). Also, it is a method of identifying the time Th exceeding 1 / 2 of the peak value of the time-concentration curve as the inflow time of the contrast agent at the pixel. The third is a method of identifying the time Ts when the time-concentration curve exceeds a certain threshold as the inflow time of the contrast agent at the pixel, which is also called TTA (Time to Arrival). Note that the characteristic quantity related to the flow is not limited to the inflow time of the contrast agent, and for example, it may be the mean transit time (MTT) of the contrast agent. In FIG. 10, the respective times T0, Th, Ts can be read from the time-concentration curve of the vascular region of interest Bv based on the X-ray images of a plurality of frames before correction. However, in the case of a normal time-concentration curve, since it is obtained on the premise that the imaging conditions do not change, the broken line (baseline) of the background region of interest Bg where the contrast agent does not reach changes substantially constantly. On the other hand, in the case of the time-concentration curve shown in FIG. 10, the broken line (baseline) of the background region of interest Bg where the contrast agent does not reach has changed, indicating that it has been affected by changes in the imaging conditions. Therefore, there is a concern that the time-concentration curve based on the X-ray image before correction may be shifted in terms of its rising shape and peak value, and the read times T0, Th, Ts may be incorrect.

[0061] In contrast, according to the first embodiment, based on the reference index and the latest index regarding the brightness of the X-ray image, by correcting the luminance value of the X-ray image with respect to the latest index, as shown in FIG. 8(b), the image luminance of the background region of interest Bg changes substantially constantly. Therefore, the time-concentration curve (not shown) based on the corrected X-ray image is not affected by changes in the imaging conditions, and the broken line (baseline) of the background region of interest Bg becomes substantially constant. Accordingly, it is possible to suppress the influence caused by changes in the imaging conditions from the change in the image density of the X-ray image over time due to the contrast agent. Also, based on the corrected X-ray image, it is possible to correctly obtain the time-concentration curves of the contrast regions such as the blood vessel region of interest Bv and the myocardial region of interest Myo, and to realize correct blood flow measurement.

[0062] Also, according to the first embodiment, the processing circuit 74 corrects the luminance value of the X-ray image with respect to the latest index so as to maintain the brightness of the X-ray image with respect to the reference index. Thereby, in addition to the effects described above, it is possible to maintain the brightness of the background region where the contrast agent does not reach among the respective regions of the corrected X-ray image.

[0063] Also, according to the first embodiment, the processing circuit 74 obtains the change ratio of the latest index with respect to the reference index, and corrects the luminance value based on the change ratio. Thereby, in addition to the effects described above, it is possible to suppress the change in the brightness of the background region where the contrast agent does not reach among the respective regions of the corrected X-ray image.

[0064] Also, according to the first embodiment, the processing circuit 74 acquires the imaging conditions of the X-ray image as an index. Thereby, in addition to the effects described above, by referring to the imaging conditions in the memory 71, it is possible to acquire the index regarding the brightness of the X-ray image without analyzing the X-ray image.

[0065] Also, according to the first embodiment, the processing circuit 74 acquires the tube current-time product as an index. Thereby, in addition to the effects described above, by referring to the tube current and pulse width in the memory 71 or the tube current-time product in the memory 71, an index can be acquired without analyzing the X-ray image.

[0066] Also, according to the first embodiment, the processing circuit 74 performs automatic brightness control to control the brightness of the X-ray image of the subject P by adjusting the imaging conditions of the X-ray image. Thereby, in addition to the effects described above, the entire X-ray image darkened by the injection of the contrast agent can be brightened.

[0067] Also, according to the first embodiment, the processing circuit 74 causes the display 72 to display an X-ray image with corrected brightness values. Thereby, in addition to the effects described above, it is possible to visually confirm that the brightness values of the X-ray image are corrected.

[0068] (Modification example) In the first embodiment, steps ST50 to ST70 are executed during the contrast imaging period to correct the brightness values of the X-ray images, but the present invention is not limited to this. For example, after the end of the contrast imaging period, steps ST50 to ST70 may be executed based on the X-ray images for each frame and the imaging conditions stored in the memory 71 or the like to correct the brightness values of the X-ray images. When correcting the brightness values after the end of the contrast imaging period, a preliminary contrast imaging for setting the region of interest in advance can be omitted. In any case, according to this modification example, the same effects as those of the first embodiment can be obtained.

[0069] Similarly, in the first embodiment, during the contrast imaging period, the X-ray image before correction and the X-ray image after correction are each displayed, but the present invention is not limited to this. For example, only the X-ray image before correction may be displayed during the contrast imaging period. Even if it is modified in this way, the same effects as those of the first embodiment can be obtained.

[0070] <Second embodiment> Unlike the first embodiment that uses imaging conditions as an indicator, the second embodiment acquires the luminance value of the background region of interest Bg that the contrast agent does not reach as an indicator. Note that the background region of interest Bg is an example of a background region that the contrast agent does not reach.

[0071] Accordingly, the acquisition function 745 of the processing circuit 74 acquires the luminance value from a part of the X-ray image instead of the imaging conditions in the above-described function. For example, the acquisition function 745 acquires the luminance value of the background region of interest Bg that the contrast agent does not reach from the generated X-ray image as an indicator. At this time, for example, the acquisition function 745 may set the background region of interest Bg based on a plurality of generated X-ray images. Also, for example, the acquisition function 745 may generate a minimum value image representing the contrast region where the contrast agent has reached from each of the plurality of X-ray images, and set the background region of interest Bg based on each minimum value image. That is, the acquisition function 745 sets the background region of interest Bg based on the fact that each minimum value image that changes with time indicates the contrast region, and the region obtained by removing the contrast region indicated by each minimum value image from the X-ray image is the background region.

[0072] Further, the correction function 746 uses the luminance value acquired by the acquisition function 745 as an indicator in the above-described function.

[0073] Other configurations are the same as those in the first embodiment.

[0074] Next, the operation in the second embodiment will be described with reference to FIGS. 11 to 13. Note that FIG. 11 is a flowchart, and FIGS. 12 and 13 are schematic diagrams. In the second embodiment, after a low-dose preliminary contrast imaging for automatically setting the background region, a main contrast imaging for performing image analysis including the creation of a time-concentration curve is performed. Also, in the second embodiment, as described above, steps ST10 to ST40, ST80, and ST90 are executed, while between steps ST30 and ST80, steps ST50, ST60A, and ST70A as shown in FIG. 11 are executed. The following will be described in order.

[0075] In step ST50, the processing circuit 74 sets a background region of interest Bg, for example, after a preliminary contrast imaging and before starting the main contrast imaging, and obtains an index related to the brightness of the X-ray image from the background region of interest Bg in the main contrast imaging. Such a step ST50 includes steps ST50-1, ST50-2, ST51A to ST53A, for example, as shown in FIG. 11. That is, the processing circuit 74 determines whether the preliminary contrast imaging has ended (ST50-1). If not, it proceeds to step ST40. If the preliminary contrast imaging has ended, it determines whether the background region has been set (ST50-2). As a result of the determination in step ST50-2, if not, it proceeds to step ST51A, and if the background region has been set, it proceeds to step ST53A.

[0076] In step ST51A, the processing circuit 74 generates a plurality of minimum value images from the X-ray images of a plurality of frames. Note that one minimum value image is generated from one frame of the X-ray image. Each minimum value image represents a contrast region such as a blood vessel region and a myocardial region where the contrast agent has reached in each X-ray image. Further, the processing circuit 74 sets a background region from the plurality of minimum value images (ST52A). For example, as shown in FIG. 12, the processing circuit 74 synthesizes each minimum value image g21,..., g22,..., g23,..., g24,..., g25,... to generate a composite image g20 including a heart region Ht equivalent to the contrast region. Further, the processing circuit 74 determines a region other than the heart region Ht in the composite image g20, and sets the background region of interest Bg as the background region based on the determination result. Further, the processing circuit 74 sets a blood vessel region of interest Bv in a part of the blood vessel region and a myocardial region of interest Myo in a part of the myocardial region according to the operation of the input interface 73 by the operator. Thereby, step ST52A ends, and the execution of step ST53A becomes possible in the main contrast imaging.

[0077] In step ST53A, the processing circuit 74 obtains the luminance values of the background region of interest Bg as indices Id0, Idn (ST53A).

[0078] At this time, the luminance value I(t) of the background region of interest Bg is obtained as a value corresponding to the time t. For example, during this contrast imaging period, when the time before the injection of the contrast agent is t1 and any time during the contrast imaging period after the start of injection is t2, the luminance values I(t1) and I(t2) of the background region of interest Bg are ideally expressed as in equations (1) and (2). Note that the luminance value I(t1) corresponds to the reference index Id0, and the luminance value I(t2) corresponds to the latest index Idn.

[0079] I(t1)= Io*exp(-μ*L) …(1) I(t2)=k*Io*exp(-μ*L) …(2) However, Io is the luminance value when there is no subject P, μ is the linear absorption coefficient, L is the thickness of the subject P, and k represents the change ratio.

[0080] When the imaging conditions are constant, since the change ratio k is 1 (k = 1), I(t1)=I(t2), and the image luminance becomes constant. When the imaging conditions change, the luminance values I(t1) and I(t2) of the background region of interest Bg where the contrast agent has not reached and the linear absorption coefficient μ does not change over time are acquired as indicators. Thereby, step ST50 ends.

[0081] In step ST60A, the processing circuit 74 calculates the change ratio of the latest index with respect to the reference index based on the reference index before the injection of the contrast agent and the latest index after the start of the injection of the contrast agent among the acquired indicators. However, the acquired indicators are the luminance values I(t1) and I(t2) of the background region of interest Bg. Therefore, the change ratio k is calculated from the formula k = I(t2) / I(t1) as the ratio of the luminance values. Also, the change ratio k is updated to a value corresponding to the change in the latest luminance value I(t2) in the background region of interest Bg for each frame of the X-ray image.

[0082] In step ST70A, the processing circuit 74 corrects the luminance value I(t2) of the X-ray image with respect to the latest index Idn based on the change ratio in the same manner as in step ST70. The corrected luminance value Ic(t2) becomes 1 / k times the luminance value I(t2) before correction, as shown in equation (3).

[0083] Ic(t2) = I(t2) / k = Io * exp(-μ * L) …(3) Note that since the linear absorption coefficient μ does not change over time, the corrected luminance value Ic(t2) of the background region of interest Bg is equal to the luminance value I(t1) before the injection of the contrast agent. Since the linear absorption coefficient μ increases according to the degree of arrival of the contrast agent, the corrected luminance value Ic(t2) of the blood vessel region of interest Bv becomes a value smaller than the luminance value I(t1) before the injection of the contrast agent. Similarly, for the corrected luminance value Ic(t2) of the myocardial region of interest Myo, it also becomes a value smaller than the luminance value I(t1) before the injection of the contrast agent according to the degree of arrival of the contrast agent. Therefore, the brightness of the entire X-ray image decreases.

[0084] Supplementary note: In such step ST70A, as shown in Fig. 13(a), the luminance value of the X-ray image before correction for the latest index after the start of injection of the contrast agent is corrected to the luminance value of the X-ray image for the reference index before the injection of the contrast agent, as shown in Fig. 13(b). As shown in Fig. 13(b), for the X-ray image after such correction, since the image luminance of the background region of interest Bg where the contrast agent does not reach changes substantially constantly, it can be directly used for image analysis.

[0085] Hereinafter, in the same manner as described above, the processing after step ST80 is executed.

[0086] As described above, according to the second embodiment, the processing circuit 74 acquires, as an index, the luminance value of the background region of interest Bg where the contrast agent does not reach from the generated X-ray image. Thus, in addition to the effect of the first embodiment, since the luminance value directly representing the brightness is acquired as an index instead of the imaging condition indirectly representing the brightness of the X-ray image, it can be expected that the corrected luminance value is maintained at a more constant value.

[0087] Further, according to the second embodiment, the luminance value of the region where the contrast agent does not reach (the region other than the heart region Ht) in the entire X-ray image is acquired, and the luminance of the entire X-ray image is corrected in the time direction so that the temporal change of the luminance value of the region where the contrast agent does not reach becomes constant. Therefore, the influence due to the change in the imaging conditions can be suppressed from the change in the luminance value in the time direction of the entire X-ray image during the contrast imaging period.

[0088] Also, according to the second embodiment, the processing circuit 74 sets the background region of interest Bg based on the plurality of generated X-ray images. Thereby, in addition to the above-described effects, it is possible to improve the accuracy of the background region of interest Bg according to the number of the plurality of X-ray images while omitting the labor of setting the background partial region Bg. Supplementary, at each time during the contrast imaging period, the region where the contrast agent does not reach is different for each frame of the X-ray image. On the other hand, the background region of interest Bg needs to be a region where the contrast agent does not reach in all X-ray images during the contrast imaging period. Therefore, it is preferable to set the background region of interest Bg based on the X-ray images of a plurality of frames from the viewpoint of accuracy.

[0089] Also, according to the second embodiment, the processing circuit 74 generates a minimum value image representing the contrast region where the contrast agent has reached from each of the plurality of X-ray images, and sets the background region of interest Bg based on each minimum value image. Therefore, in addition to the above-described effects, it is possible to improve the accuracy of the background region of interest Bg according to the number of the plurality of X-ray images used for generating the minimum value image. Further, since the background region of interest Bg is set by the minimum value image, there is no concern that the operator sets the background region of interest Bg so as to include a part of the contrast region, and the reliability of the background region of interest Bg can be ensured.

[0090] (Modification example) In the second embodiment, the background region of interest Bg is set based on each minimum value image. In contrast, in the modification example of the second embodiment, as shown in FIG. 4, the background region of interest Bg is set based on the change in the luminance value of each region in the X-ray image. Note that the background region of interest Bg is an example of a background region where the contrast agent does not reach.

[0091] Accordingly, in the acquisition function 745 of the processing circuit 74, in the above-described function, a region with a substantially constant luminance value is specified from a plurality of X-ray images, and a part of the specified region is set as the background region of interest Bg.

[0092] Other configurations are the same as those in the second embodiment.

[0093] According to the configuration as described above, similar to the second embodiment, steps ST10 to ST40 and ST60A to ST90 are executed. On the other hand, between step ST30 and ST60A, step ST50 as shown in FIG. 14 is executed. Note that in step ST50 shown in FIG. 14, steps ST51B and ST52B regarding the acquisition of the background region are different from those in FIG. 11. The following is a description in order.

[0094] In step ST50, the processing circuit 74 executes the determinations of steps ST50-1 and ST50-2 as described above. As a result of the determination in step ST50-2, if the result is negative, the process proceeds to step ST51B, and if the background region is set, the process proceeds to step ST53B.

[0095] In step ST51B, the processing circuit 74 acquires the temporal change of the luminance value of each pixel from a plurality of frames of X-ray images. Further, the processing circuit 74 sets the background region from the temporal change of the luminance value of each pixel (ST52B). For example, as shown in FIG. 4, the processing circuit 74 specifies a region in which the temporal change of the luminance value of each pixel from a plurality of frames of X-ray images is substantially constant, and sets a part of the specified region, that is, the background region of interest Bg, as the background region. Thereby, step ST52B ends, and the execution of step ST53B becomes possible.

[0096] In step ST53B, the processing circuit 74 acquires the luminance value of the background region of interest Bg as an index. At this time, the luminance value I(t) of the background region of interest Bg is acquired as a value corresponding to the time t, similar to the second embodiment.

[0097] Hereinafter, similar to the second embodiment, the processing after step ST60A is executed.

[0098] Therefore, according to the modification of the second embodiment, the processing circuit 74 identifies a region with substantially constant luminance values from a plurality of X-ray images, and sets a part of the identified region as the background region of interest Bg. As a result, while omitting the load of generating the minimum value images g21 to g25 and the composite image g20 described above, the same effect as that of the second embodiment can be obtained.

[0099] Also, in the second embodiment and its modification, steps ST50 to ST70 are executed during the contrast imaging period including the preliminary contrast period and the main contrast period to correct the luminance values of the X-ray images, but it is not limited thereto. For example, the preliminary contrast imaging for setting the background region may be omitted, and after the end of the contrast imaging period, based on a plurality of frames of X-ray images stored in the memory 71 or the like, steps ST50 to ST70 may be executed to correct the luminance values of the X-ray images. In this case, among steps ST50, steps ST50-1 and ST50-2 related to the determination of the end of the preliminary contrast imaging and the determination of the setting of the background region are omitted. Even if modified in this way, the same effect as that of the second embodiment and its modification can be obtained.

[0100] Similarly, in the second embodiment and its modification, step ST80 of displaying the pre-correction X-ray image and the post-correction X-ray image respectively during the contrast imaging period is executed, but it is not limited thereto. For example, in step ST80, only the pre-correction X-ray image may be displayed during the contrast imaging period. Even if modified in this way, the same effect as that of the second embodiment and its modification can be obtained.

[0101] According to at least one of the embodiments described above, it is possible to suppress the influence due to the change in the imaging conditions from the temporal change in the image density of the X-ray image by the contrast agent.

[0102] The term "processor" used in the above description means, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA), etc.). When the processor is, for example, a CPU, the processor realizes its function by reading and executing a program stored in a storage circuit. On the other hand, when the processor is an ASIC, instead of storing a program in a storage circuit, the function is directly incorporated as a logic circuit in the circuit of the processor. Note that each processor of the present embodiment is not limited to being configured as a single circuit for each processor, and a plurality of independent circuits may be combined to be configured as one processor to realize its function. Further, a plurality of components in FIG. 1 may be integrated into one processor to realize its function.

[0103] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the invention described in the claims and its equivalent scope.

Explanation of reference numerals

[0104] 1 X-ray diagnostic apparatus 10 Imaging device 11 High voltage generator 12 X-ray generating section 13 X-ray detector 14 C-arm 141 State detector 142 C-arm drive device 40 Injector 50 Bed device 51 Base 52 Bed drive device 53 Top plate 54 Support frame 70 Console device 71 Memory 72 Display 73 Input interface 74 Processing circuit 741 System control function 742 Drive control function 743 Imaging control function 744 Image processing function 745 Acquisition function 746 Correction function 747 Display control function 76 Network interface 77 Medical image processing device Bv Vascular region of interest Myo Myocardial region of interest Bg Background region of interest

Claims

1. An X-ray tube that irradiates an object into which a contrast agent is injected with X-rays, an X-ray detector that detects X-rays irradiated from the X-ray tube and transmitted through the object, an image generation unit that generates an X-ray image based on the output of the X-ray detector, an acquisition unit that acquires an index related to the brightness of the X-ray image, a correction unit that corrects the luminance value of the X-ray image with respect to the latest index based on the reference index before injection of the contrast agent and the latest index after the start of injection of the contrast agent among the acquired indices, An X-ray diagnostic apparatus comprising:

2. The X-ray diagnostic apparatus according to claim 1, wherein the correction unit corrects the luminance value so as to maintain the brightness of the X-ray image with respect to the reference index.

3. The X-ray diagnostic apparatus according to claim 2, wherein the correction unit obtains a change ratio of the latest index with respect to the reference index and corrects the luminance value based on the change ratio.

4. The X-ray diagnostic apparatus according to any one of claims 1 to 3, wherein the acquisition unit acquires the imaging conditions of the X-ray image as the index.

5. The X-ray diagnostic apparatus according to any one of claims 1 to 3, wherein the acquisition unit acquires the tube current-time product as the index.

6. The X-ray diagnostic apparatus according to any one of claims 1 to 3, wherein the acquisition unit acquires, as the index, the luminance value of a background region that the contrast agent does not reach from the generated X-ray image.

7. The X-ray diagnostic apparatus according to claim 6, wherein the acquisition unit sets the background region based on a plurality of generated X-ray images.

8. The X-ray diagnostic apparatus according to claim 7, wherein the acquisition unit generates, from each of the plurality of X-ray images, a minimum value image representing a contrast region reached by the contrast agent, and sets the background region based on each of the minimum value images.

9. The X-ray diagnostic apparatus according to claim 7, wherein the acquisition unit specifies a region having a substantially constant luminance value from the plurality of X-ray images, and sets a part of the specified region as the background region.

10. A photographing control unit that executes automatic brightness control for controlling the brightness of an X-ray image of an object by adjusting the photographing conditions of the X-ray image, The X-ray diagnostic apparatus according to any one of claims 1 to 3, further comprising:

11. A display control unit that causes a display unit to display the X-ray image whose luminance value has been corrected, The X-ray diagnostic apparatus according to any one of claims 1 to 3, further comprising:

12. Irradiating an object into which a contrast agent is injected with X-rays, detecting the X-rays that have been irradiated and transmitted through the subject; generating an X-ray image of the subject based on the detection result of the X-rays; acquiring an index related to the brightness of the X-ray image; correcting the luminance value of the X-ray image with respect to the latest index based on the reference index before injection of the contrast agent and the latest index after the start of injection of the contrast agent among the acquired indices; A correction method comprising the above.

Images